1. Field of the Invention
The present invention relates to a driven wheel slip controlling system for a vehicle for controlling to increase or decrease a driven wheel torque in order to prevent an excessive slip of a driven wheel.
2. Description of the Related Art
In order to prevent the driven wheel from excessively slipping at the time of sudden start or sudden acceleration of the vehicle, there is a conventional technique, known as a traction control system, for decreasing an engine output to decrease the driven wheel torque to avoid the slipping of the driven wheel when a slip rate of the driven wheel exceeds a predetermined threshold value.
Further, when a driver of the vehicle downshifts, the driven wheel tends to lock-up because of engine braking. For this reason, the driven wheel may slip (a deceleration slip, i.e., skid) with respect to a road surface causing loss of control of the vehicle. In order to prevent such slippage, there is also a known technique to avoid the deceleration slip by controlling a throttle valve to open to increase the driven wheel torque when a locking of the driven wheel due to the downshifting is detected.
However, in the latter technique, the throttle valve is opened after detection of the locking of the driven wheel due to the downshifting. Therefore, there is a problem that the deceleration slip cannot swiftly be dissipated due to a delay of the control of the throttle valve, resulting in loss of control of the vehicle.
Furthermore, when the driver conducts either an upshifting or a kickdown, the driven wheel torque may temporarily be increased and the driven wheel may develop an acceleration slip. In such a case, the acceleration slip cannot swiftly be dissipated due to delay of the control of the throttle valve resulting in the likelihood of loss of control of the vehicle.